Sheet forming machine

ABSTRACT

A sheet forming machine which has a pair of coating rolls, a driving mechanism for rotating the coating rolls, angle detectors for detecting rotation angles of the coating rolls, level change detectors for detecting change patterns of levels of circumferential points of the coating rolls, and a shaft mover for moving at least one of the coating rolls to keep a constant space between the coating rolls.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet forming machine which forms a slurry material into a sheet by use of a pair of coating members.

2. Description of Related Art

Generally, ceramic green sheets are made by casting. In the casting, a slurry material is continuously poured onto a traveling organic film as a sheet with a specified thickness, and the material on the organic film is dried and rolled up during the travel of the organic film. A sheet forming machine is used to carry out the casting.

Conventionally, a sheet forming machine is provided with a reverse roll coater as shown in FIG. 3, a knife coater as shown in FIG. 4 or the like so as to continuously pour a slurry material onto an organic film.

The reverse roll coater of FIG. 3 has a pair of coating rolls R₁ and R₂, and a back-up roll R₃. The rolls R₁, R₂ and R₃ are rotated in the same direction (clockwise direction in this example). The coating rolls R₁ and R₂ are arranged opposite each other with a specified space H in-between. While a slurry material S is poured through the space between the coating rolls R₁ and R₂, an organic film B is continuously fed by the back-up roll R₃. Thereby, the material S poured through the space between the coating rolls R₁ and R₂ comes onto the organic film B, and the material S is made into a sheet F.

The knife coater of FIG. 4 has a coating knife N, a coating roll R₂ and a back-up roll R₃. The rolls R₂ and R₃ are rotated in the same direction (clockwise direction in this example). While a slurry material S is poured through the space H between the coating knife N and the coating roll R₂, an organic film B is continuously fed by the back-up roll R₃. Thereby, the material S poured through the space between the knife N and the roll R₂ comes onto the organic film B, and the material S is made into a sheet F.

In the reverse roll coater of FIG. 3, the space H between the coating rolls R₁ and R₂ serves as an inlet of the material S and is an important factor which determines the thickness of the sheet F. Likewise, in the knife coater of FIG. 4, the space H between the coating knife N and the coating roll R₂ is an important factor which determines the thickness of the sheet F. Therefore, in order to make a sheet F with a uniform thickness, the space H must be kept constant while the coating rolls R₁ and R₂ are rotating.

However, it is difficult to produce exactly cylindrical rolls R₁ and R₂ because of errors in processing, and the rolls R₁ and R₂ generally have out-of-roundness of about several micrometers to scores of micrometers. Also, even if an exact cylindrical roll can be produced, because of errors in providing a shaft to the cylindrical roll, eccentricity is generated. Accordingly, while the coating rolls R₁ and R₂ are rotating, the level of the circumferential point of each roll which faces the other roll changes periodically. Consequently, the space H between the rolls R₁ and R₂ in the reverse roll coater of FIG. 3 or the space H between the knife N and the roll R₂ in the knife coater of FIG. 4 changes during the rotation of the coating rolls R₁ and R₂.

The change of the space H is described in connection with the reverse roll coater of FIG. 3. As shown in FIG. 2a, the coating roll R₁ is rotated at a relatively low speed, and the level of the circumferential point facing the roll R₂ changes periodically as indicated by a curve C₁. The coating roll R₂ is rotated at a higher speed, and the level of the circumferential point facing the roll R₁ changes periodically as indicated by a curve C₂. The change of the space H between the rolls R₁ and R₂ is indicated as the change of the distance between the curves C₁ and C₂. The space between the rolls R₁ and R₂ is H₁ at a moment and is H₂ (≠H₁) at another moment.

In accordance with the change of the space H between the rolls R₁ and R₂, the thickness of the material S poured through the space H changes. Thus, it is difficult to form a sheet F with a uniform thickness.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sheet forming machine which can form a sheet with a uniform thickness by keeping a constant space between a pair of coating members which serves as an inlet of a material.

A sheet forming machine according to the present invention comprises: a pair of coating members, at least one of which is a coating roll; driving means for rotating the coating roll; angle detecting means for detecting a rotation angle of the coating roll; level change detecting means for detecting a change pattern of a level of a circumferential point of the coating roll; and moving means for moving one of the coating members so as to keep a constant space between the coating members.

In the structure, the angle detecting means detects the rotation angle of the coating roll. The level change detecting means detects the level of a circumferential point of the coating roll during its rotation and recognizes a change pattern of the level.

In accordance with an output of the angle detecting means and an output of the level detecting means, the moving means moves at least one of the coating members such that a constant space can be kept between the pair of coating members.

In this way, the space between the coating members, which serves as an inlet of a material, can be kept constant, and consequently, a sheet with a uniform thickness can be formed. With this arrangement, it is not necessary to improve the production accuracy of coating rolls, and an increase in the production cost of coating rolls can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of the present invention will be apparent from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a sheet forming machine according to the present invention;

FIGS. 2a and 2b are graphs showing change patterns of the levels of circumferential points of a pair of coating rolls during rotation of the coating rolls;

FIG. 3 is a side view of a conventional reverse roll coater provided in a sheet forming machine; and

FIG. 4 is a side view of a conventional knife coater provided in a sheet forming machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is described with reference to the accompanying drawings.

FIG. 1 is a schematic view of a sheet forming machine according to the present invention. The sheet forming machine has a reverse roll coater, and the reverse roll coater comprises a pair of coating rolls R₁ and R₂, and a back-up roll (not shown). The coating rolls R₁ and R₂ are connected to a drive mechanism 20 to rotate on respective shafts. The coating rolls R₁ and R₂, and the back-up roll are rotated in the same direction.

The coating rolls R₁ and R₂ are arranged opposite each other with a specified space in-between. While a slurry material is poured through the space between the coating rolls R₁ and R₂, an organic film is continuously fed by the back-up roll. Thereby, the material poured through the space between the rolls R₁ and R₂ comes onto the organic film, and the material is made into a sheet.

The coating rolls R₁ and R₂ are provided with level detectors 1₁ and 1₂ and angle detectors 2₁ and 2₂, respectively. The level detectors 1₁ and 1₂ detect the levels of circumferential points of the respective rolls R₁ and R₂ during rotation of the rolls R₁ and R₂, and the angle detectors 2₁ and 2₂ detect the rotation angles of the respective rolls R₁ and R₂.

In the embodiment, the level detectors 1₁ and 1₂ are differential transforming contact type sensors. However, non-contact type gap detectors can be used as the level detectors 1₁ and 1₂. Each of the level detectors 1₁ and 1₂ can be set to detect any circumferential point of each roll.

The level detectors 1₁ and 1₂ are connected to a level change calculator 3. From outputs of the level detectors 1₁ and 1₂, the level change calculator 3 calculates change values of the levels of the circumferential points of the rolls R₁ and R₂ during rotation of the rolls R₂ and R₂.

In the embodiment, only a single level detector is provided to each of the coating rolls R₁ and R₂. However, in order for more accurate detection, two or more level detectors may be provided to each of the coating rolls R₁ and R₂ to detect the levels of a plurality of circumferential points of each roll.

The angle detectors 2₁ and 2₂ are, in the embodiment, rotary encoders fitted to the shafts of the coating rolls R₁ and R₂.

Further, to the coating roll R₁, shaft movers 4₁ and 4₂ are provided. The shaft movers 4₁ and 4₂ move the shaft of the coating roll R₁ in the radial direction to keep the space between the coating rolls R₁ and R₂ constant.

The shaft movers 4₁ and 4₂ comprise a pair of actuators 6₁ and 6₂ of an electric, hydraulic, pneumatic or piezoelectric type, and actuator drivers 8₁ and 8₂ which are connected to the actuators 6₁ and 6₂ respectively.

Numeral 12 denotes a controller which has a microcomputer. The controller 12 receives change values of the levels of the circumferential points of the coating rolls R₁ and R₂ from the change value calculator 3 and rotation angles of the rolls R₁ and R₂ from the angle detectors 2₁ and 2₂. From these values, the controller 12 calculates change values of the levels of the mutually facing circumferential points of the coating rolls R₁ and R₂ at various rotation angles. Then, data about the change values at various rotation angles are stored in a memory 10. The memory 10 comprises a disk unit, a RAM, etc. During sheet forming, the controller 12 reads the rotation angles of the coating rolls R₁ and R₂ detected by the angle detectors 2₁ and 2₂, and judges the change values of the levels of the mutually facing circumferential points of the rolls R₁ and R₂ at the detected rotation angles, referring to the data stored in the memory 10. Then, the controller 12 calculates a shaft moving value to keep the space H between the coating rolls R₁ and R₂ at a specified value, and transmits the shaft moving value to the actuator drivers 8₁ and 8₂.

Next, sheet forming out of a slurry material by use of the sheet forming machine is described.

Before sheet forming, the coating rolls R₁ and R₂ are rotated to collect data to be stored in the memory 10. More specifically, during the rotation, outputs of the angle detectors 2₁ and 2₂ and outputs of the level detectors 1₁ and 1₂ are read by the controller 12, and data about change values of the levels of the mutually facing circumferential points of the rolls R₁ and R₂ at various rotation angles of the rolls R₁ and R₂ are made from the outputs and stored in the memory 10.

For example, the rotation of the coating rolls R₁ and R₂ is recognized as shown by the graph of FIG. 2a. The coating roll R₁ is rotated at a relatively low speed, and the change of the level of a circumferential point of the roll R₁ is detected as a pattern indicated by a curve C₁. The coating roll R₂ is rotated at a higher speed, and the change of the level of a circumferential point of the roll R₂ is detected as a pattern indicated by a curve C₂. Data shown as the curves C₁ and C₂ are stored in the memory 10.

During sheet forming, the controller 12 reads the rotation angles of the coating rolls R₁ and R₂ from outputs of the angle detectors 2₁ and 2₂. Then, the controller 12 judges the change values of the levels of the mutually facing circumferential points of the coating rolls R₁ and R₂ at the detected rotation angles, referring to the data stored in the memory 10.

From the change patterns, the controller 12 judges the change values of the levels of the mutually facing circumferential points of the coating rolls R₁ and R₂. More specifically, the change value of the level of the circumferential point of the coating roll R₁ is judged referring to the curve C₁, and the change value of the level of the circumferential point of the coating roll R₂ is judged referring to the curve C₂. In this embodiment, the shaft movers 4₁ and 4₂ are provided only to the coating roll R₁. From the change values of the coating rolls R₁ and R₂, the controller 12 calculates a shaft moving value which determines the moving amount of the shaft of the coating roll R₁. Then, the controller 12 transmits data about the shaft moving value to the actuator drivers 8₁ and 8₂.

Thereby, as shown in FIG. 2b, the shaft of the coating roll R₁ is moved such that the level of the circumferential point of the coating roll R₁ facing the coating roll R₂ changes in synchronization with the change of the level of the circumferential point of the coating roll R₂ facing the coating roll R₁. Thus, the space H between the coating rolls R₁ and R₂ can be kept constant.

The space between the coating rolls R₁ and R₂ is H₀ at a moment, and the space therebetween at another moment is H₀.

Consequently, although the coating rolls R₁ and R₂ are out of round and eccentric, a sheet with a uniform thickness can be formed.

Although in the embodiment, the shaft movers 4₁ and 4₂ are provided only to the coating roll R₁, it is possible to provide the shaft movers to both the coating rolls R₁ and R₂. In that case, the shafts of the coating rolls R₁ and R₂ are moved so as to offset the changes of the levels of the mutually facing circumferential points of the respective rolls R₁ and R₂. Thereby, the space between the coating rolls R₁ and R₂ can be kept constant.

In the embodiment, the present invention is applied to a reverse roll coater. However, the present invention is applicable to a knife coater which has a coating knife N and a coating roll R₂. In this case, the level detector 1₂ and the angle detector 2₂ may be provided only to the coating roll R₂, and the shaft movers 4₁ and 4₂ may be provided to at least one of the knife N and the roll R₂.

In the embodiment, data about change values of the levels of the mutually circumferential points of the coating rolls R₂ and R₂ are stored in the memory 10 before sheet forming, and the data are used for control of the shaft movers 4₁ m and 4₂ during sheet forming. However, it is possible to control the shaft movers 4₁ and 4₂ in accordance with outputs of the level detectors 1₁ and 1₂ and outputs of the angle detectors 2₁ and 2₂ which are sent during sheet forming.

Although the present invention has been described in connection with the preferred embodiment, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the present invention. 

What is claimed is:
 1. A sheet forming machine for forming a slurry material into a sheet, comprising:a pair of coating members which are arranged opposite each other with a nominal space in-between, at least one of the coating members being a coating roll, a slurry material being fed through the space between the coating members to be formed into a sheet; a drive connected to said coating roll for rotating the coating roll; an angle detector for detecting a rotation angle of the coating roll; a level change detector disposed in communication with said coating roll for detecting a change pattern of a level of a circumferential point of the coating roll during rotation of the coating roll; and a mover connected to said coating roll for moving the coating roll in accordance with an output of the angle detector and an output of the level change detector so as to keep the space between the coating members constant.
 2. A sheet forming machine as claimed in claim 1, wherein:both coating members are coating rolls; the angle detector detects respective rotation angles of the coating rolls; the level change detector detects change patterns of levels of circumferential points of the coating rolls during rotation of the coating rolls; and the mover moves at least one of the coating rolls.
 3. A sheet forming machine as claimed in claim 1, wherein the coating members include a coating roll which is rotated in one direction and a coating knife which is disposed opposite the coating roll at a specified space from the coating roll. 